glacial runoff provides water for 1 1/2 billion people, mostly in south america, china, and india. >> in the medium term-- let's say, depending on the size of the glacier, 30 years, just a few decades-- the glacier will start to waste away in such a degree that you will see the runoff, the glacial melt coming from that glacier starting to decline. >> and these cities around the world will be starved for water. >> exactly, so that's a major issue. and we see now the first impacts. >> we wanted to see the evidence of warming nearer the bottom of the world, so we set sail ast city south, ushuaia, argentina, on a two-day voyage to antarctica. it's more than 1,000 miles from glacier o'higgins in patagonia and across the drake passage to the antarctic peninsula. here, we found there's green where the white used to be. on the coast in summer, there's grass where the scientists used to ski. this is paradise cove. it's home to fur seals, lazy elephant seals, and the chinstrap penguin. there's the chin strap right there, right under the eye. american biologists sue and wayne trivelpiece were th